Large code bases themselves don’t have to be confusing though. I worked as a contractor at Google and their system was very dev friendly with almost everything is available/viewable in a large repo with good editing and build tools.
I hope those 250 developers are split up on small teams, with small manageable projects.
Most of my jobs have had very straight forward goals of what needs done next, with an endless backlog of already prioritized work. There has very rarely been much documentation around anything though.
This company is more vague high level goals that teams have the ability to figure out any work they want to do that furthers that goal, but there is a very high bar for documentation before, during, and after features are done. Even git commits have a very rigid structure to them!